The present invention relates to electric power plant boilers and more particularly to those using solid fuels containing carbon materials.
In general, this type of boiler uses air as the oxidizer. This technology is proven, but it must contend with the new requirements to capture CO2 in the flue gases issuing from the combustion of these carbon materials before release into the atmosphere.
The CO2 present in the flue gases can obviously be selectively extracted, but because of their low content (15% by volume), this postcapture proves to penalize efficiency and is extremely costly.
To decrease the quantity of CO2 produced, it is known from the proprietor's patents U.S. Pat. Nos. 6,202,574 and 6,505,567 to carry out the combustion using oxygen, no longer diluted in nitrogen as in the air, but oxygen diluted in recycled CO2. The boiler thereby only produces a gas stream of CO2 and water vapor, which can be dried and liquefied for transport to a subsequent use of the CO2 or for underground sequestration.
In this case of O2/Co2 combustion, the step of selective extraction of the CO2 present in the flue gases, which involves high energy consumption, is eliminated, but a new energy penalization appears, deriving from the electric power consumption associated with the cryogenic production of oxygen, which is the only method available today for producing large quantities of oxygen. The power consumption due to oxygen production is so high as to risk making the oxycombustion technology economically prohibitive.
The high temperature oxygen transport membranes available today are suitable for extracting oxygen from the air. They are used to feed burners like, for example, those described in patent application WO02/077419 or the patents U.S. Pat. Nos. 6,539,719 and 96,562,104. However, these membranes can only be used in gas medium. Moreover, the oxygen issuing from the membrane must be flushed with an auxiliary gas.